ABSTRACT The Family Smoking Prevention and Tobacco Control Act (FSPTCA) provides the U.S. Food & Drug Administration (FDA) the authority to regulate e-cigarette (e-cig) marketing. The FDA specifically has the authority to restrict e-cig marketing that promotes e-cig/cigarette use among young people. Currently, the e-cig marketing is largely unregulated. This study?s goal is to generate evidence that the FDA can use to regulate e- cig marketing effectively. At present, little is known about the mechanisms of how e-cig marketing is related to young people?s e-cig and dual (e-cig and cigarette) use behavior. In particular, the social processes of e-cig marketing?s influence on behavior have been poorly understood. In the area of tobacco marketing research in general, extant findings are limited to the extent of showing that peer and family influence, vis--vis marketing, has independent and stronger effect on increased tobacco product use among young people. This has led the tobacco industry to argue that tobacco marketing?s influence on tobacco use initiation and maintenance is negligible compared with social influence. Scientific evidence showing that social processes are part of the mechanism of marketing?s influence on young adults? e-cig/dual use would help the FDA argue in favor of strongly regulating e-cig marketing that targets young people. Social influence among young adults may occur through interactional social networks, comprised of individuals who interact with each other on a reular basis; and within a larger context of reputational groups or peer ?crowds,? groups with subcultural underpinnings that are seen as collectives with shared lifestyle preferences and behaviors (e.g., Goth, Hipster, Hip Hop). The tobacco industry is long suspected of segmenting and targeting young adults based on peer crowds, although no empirical evidence currently exists showing that some peer crowds are actually more receptive to tobacco or e-cig marketing than others and as a result show higher tobacco or e-cig use behavior. Further, ?vape- shops? (specialty shops for e-cig products) appear to utilize actual social networks and social media (e.g., Instagram, Facebook) to reach young people. This longitudinal study will collect 3 waves of data at 6-month intervals from multi-ethnic community (2-year) college students (N = 2000) in order to: 1) inform the FDA about peer crowds that are particularly receptive to e-cig marketing?s influence on behavior; and 2) generate the evidence that e-cig marketing influences young adults? actual social network ties so as to result in increased e- cig and dual use. We will collect ego-centric social networks data, which will include data on network members? ties to vape shops and their social media using habits. In summary, the high quality data we will generate will help the FDA 1) restrict e-cigarette marketing that targets vulnerable young adult peer crowds; 2) develop anti- e-cig social marketing campaigns for vulnerable peer crowds; and 3) restrict marketing that promotes social network ties conducive to e-cig/dual use.